Reseach On The Dynamic Response In Liquid Crystal Displays

Liquid crystal displays were widely used in many fields because of its light weight, thin panel and low power consumption, however, its response speed is not favorable. Some typical liquid crystal display modes were researched in detail using the classical dynamical theory, the results show that the factors affect the response time include the rotational viscosity and elastic parameters of liquid crystal, the thickness of the liquid crystal layer and the driven voltage. For the liquid crystal display mode with complex configuration, most people gave the theoretical analysis on the results of numerical simulation or experimental data. In this thesis, the dynamic responses of liquid crystal display modes were researched through the small deformation approximation and the continuum elastic theory. The effects of surface anchoring and surface viscosity on the dynamical response of liquid crysal display were researched, the response times of the in-plane switching, optically compensated bend and vertical alignment liquid crystal display modes were studied in detail, moreover, the response mechanism of the dual frequency, ferroelectric and blue phase liquid crystal display modes with submillisecond response times were analyzed.The anchoring energy's effect on the director response time is studied by using effective cell gap and solving eigenvalue method. The dynamic responses of the liquid crystal near the substrates in the fast and slow response processes were analyzed in detail, and the effect of surface rotational viscosity is determined by the numerical simulation. The relationships of the director and optical response times were shown from the theoretical analysis, in the pure twist, splay and bend deformations. From the results, the optical decay response time of the splay and bend deformation is improved 2X at least than that of the twist deformation. In the cell with the three deformations, the optical response time is also determined by comparing the response times of the twist and splay-bend deformation.The effects of the rubbing angle, twist and super twist configuration on the response times were researched, and the equations of response times were obtained. The response time of the super twist configuration has four times faster than that of the conventional configuration from the theoretical analysis and numerical simulation of the dynamic response. The response mechanism of double fringe field switching driven homogeneous alignment liquid crystal is researched comparing with in-plane switching mode, and the optical characteristics of this mode is analyzed.The critical voltage and transition voltage of the splay to bend transition, and the response mechanism in the bend state were studied in the optically compensated bend liquid crystal display mode. The analytical equation to calculate the critical voltage is derived, the transition voltage and the transitional process are simulated, and moreover the transitional process can be used to measure the surface rotational viscosity. The equations of the response time were derived and the fast response mechanism was summarized.The difference of the response time for the vertical alignment liquid crystal display mode with negative and positive dielectric liquid crystal material were researched. The response time of the cell with negative liquid crystal is similar to that of the classical vertical alignment mode. The in-plane switching vertical alignment cell with positive liquid crystal is same as that of the cell with negative liquid crystal. The vertical alignment cell driven by the tri-layers electrodes, the electric field has an effect in the rise and decay processes, the decay response time is derived. In the double fringe field switching vertical alignment mode, the period of liquid crystal deformation in the transversal direction is less than the thickness of liquid crystal layer, and instead of the cell gap in lognitudinal direction, shows the cell gap effect on the response time, the equation of the decay response time is theoretically derived.The dynamic response mechanism of dual frequency liquid crystal, ferroelectric liquid crystal and blue phase liquid crystal modes were analyzed. The equations to calculate the response times of the dual frequency liquid crystal display are analyzed through the theoretical analysis. Through comparing the dielectric force and the force between the spontaneous polarization and the electric field, the fast response mechanism of the ferroelectric liquid crystal is clear. The threshold voltage and the response time of the blue phase liquid crystal mode were theoretically analyzed, and numerically simulate the electro-optic characteristics using a simple model.